1. Field of the Invention
The present invention relates to a camera system, and more precisely, it relates to a camera system of an automatic focusing single lens reflex camera having an automatic focusing taking lens with a microcomputer.
2. Description of Related Art
In recent single lens reflex cameras, an automatic focusing devices are usually provided. Frequently, a TTL phase difference detection type of focus detecting means is provided in a single lens reflex camera to detect a focus thereof. The TTL phase difference detection type of focus detecting device calculates a deviation (amount of defocus) of an image plane from a film plane which is caused by the phase difference between the two divided images of an object to be taken which are formed through a taking lens (photographing lens). The necessary displacement of the focusing lens within the taking lens is calculated in accordance with the amount of defocus so that the focusing lens is moved to a focal point by a focusing motor through the calculated displacement.
The relationship between the amount of defocus and the displacement of the focusing lens depends on the taking lens and varies in accordance with the aberration of the photographing lens. To this end, in a conventional single lens reflex camera, the photographing lens (interchangeable lens) is provided with a memory means (e.g., ROM) in which lens data peculiar to the photographing lens, such as data (K value data, etc.) relating to the amount of defocus and displacement of the focusing lens is stored. A microcomputer provided in the camera body has a data communication function in which the lens data stored in the ROM of the photographing lens is read. The K value data referred to herein means a constant of a unit displacement of an image plane (focusing plane) which is characteristic of the taking lens and the number of revolutions of the AF motor.
Recently, photographing lenses in automatic focusing (AF) single lens reflex cameras have used a zoom lens in which the K value data varies in accordance with the focal length f thereof. To this end, a focal length detecting means is provided on the zoom lens to detect the present focal length, and the K value data corresponding to the focal lengths is stored in the lens ROM.
However, control of the focal length detecting means and retrieval of the K value data must be carried out by the microcomputer of the camera body (body microcomputer). This increases the communication time and load on the body microcomputer.
Generally speaking, there is always some degree of aberration in a photographing lens. For instance, there is chromatic aberration (lateral and longitudinal magnification aberrations), spherical aberration, astigmatism, coma, curvature of the field, distortion, etc. These aberrations have a large influence on the TTL automatic focus adjustment, and accordingly, it is preferable to make the necessary corrections, using the aberrations.
However, if all aberration data corresponding to the plurality of focal lengths f is stored in the lens ROM in a known page-memory system, it is necessary to use a large capacity lens ROM, resulting in an increased load on the body microcomputer and increased operation time.